Although pulsatile GnRH secretion has been well-characterized across the normal menstrual cycle of young women and in the postmenopausal years after cyclic ovarian function has ceased, little is known about the neuroendcrine dynamics of the perimenopausal transition that lead to the striking difference in GnRH secretion between the reproductive and postreproductive years. In contrast, symptoms that herald the onset of menopause have been widely studied in both patient samples and nonclinical populations but never examined within the context of a defined neuroendocrine milieu. Further, the action of sex steroid replacement therapy on the perimenopausal neuroreproductive axis has not been studied despite the growing trend to initiate hormone replacement at an earlier age. In premenopausal women with normal ovulation, we have shown subtle changes in gonadotropin secretion prior to any aging effects on ovarian sex steroid concentrations. The overall goal of the current study is to better understand the neuroendocrine mechanisms that give rise to the cessation of ovulation and the associated sequelae of suppressed ovulatory function.